In high current voltage regulators used in laptop, desktop, server and telecom applications, adaptive voltage positioning (AVP) control is widely used to achieve good transient performance and reduce load power consumption. FIG. 1A illustrates the basic principle of AVP, wherein Vout represents the output voltage of the voltage regulator, Iout represents the output current of the voltage regulator and Vref represents a reference voltage. As shown in FIG. 1, the output voltage Vout decreases when the output current Iout increases. The relationship between the output voltage Vout ad the output current Iout can be expressed as:Vout=Vref−Rdroop*Iout  (1)wherein Rdroop represents the slope.
FIG. 1B compares load transient response of voltage regulators with and without AVP. As shown in the figure, for voltage regulators without AVP, because of undershoot and overshoot at the output voltage Vout during load transient period, only half of the voltage tolerance window can be used. While in voltage regulators with AVP, the output voltage Vout is controlled to be slightly higher than a minimum value Vmin at full load, and a little bit lower than a maximum value Vmax at light load. As a result, the entire voltage tolerance window can be used during load transient period, which allows a smaller output capacitor in the voltage regulator. Furthermore, since the output voltage Vout with AVP decreases when the output current Iout increases, the output power at full load is degraded, which greatly facilitates the thermal design.
FIG. 2 schematically illustrates a widely used prior art wherein AVP is achieved by a current K0*Iout flowing through an external resistor R1. In this prior art, the relationship between the output voltage Vout and the output current Iout can be expressed as:Vout=Vref−R1*K0*Iout  (2)The slope Rdroop can be expressed as:Rdroop=R1*K0  (3)
As shown in equation (3), the slope Rdroop is determined by the external resistor R1. It is hard to be adjusted on-line during system debugging and hard to fulfill the requirement of different applications.